I wish.

Maybe we can beg Casio to build a few!
Who's with me?

Well, I doubt it could be done now after the fact, but it would have been nice if it had been designed with that in mind.

Maybe something like the Bose SoundLink Bluetooth Mobile speaker II or the mini version would sit comfortably on the battery cover. The battery is rechargeable, too, and so it doesn't necessarily have to be plugged in.

Thanks for the answer voxpops!
Gives me a little confidence that the PX-5S will be the right choice for me.
I have a little Logitech UE speaker that probably could double as a monitor for small jams, but im pretty sure it stops there, haha.

What monitor are you using with it, voxpops?
I am concidering a Rokit 5 monitor. Hopefully one will do for my little room.

The Rokit 5's are nice monitors, but depending on the sounds you want to create you might want a subwoofer too. I have the Rokit 5's and use them mostly for recording but I have used them on my MOX8.

I'm currently using a Roland CM-220 setup and it sounds great! The speakers will mount on standard microphone stands and I have used them live without issue. They can be real loud if needed.
CM-220 Link

There is also a less powerful version that would work just as well in the home studio. CM-110 Link

Deltron, I have Yamaha HS80M monitors for home use. They're chunky, but very good with regard to fidelity (and don't require a sub). Otherwise, I use either a pair of Roland CM30 monitors for light stage/rehearsal use, a Roland SA300 stage amp for gigs, or Mackie SRM350s.

I'm still trying to learn to love the piano sample in the PX. It has quite a realistic tone to it, but those plinky notes still bug the heck out of me. They're not so noticeable in chords/octaves, but stand out with flashing beacons on them during single note runs. If you're trying to play a lyrical melody line, they really grate. Mike Martin's revised piano patch helps smooth them out, but also affects the attack adversely in lower ranges. However, my personal preference may not be the same as yours. A number of people find the metallic attack at high velocities in the Roland SN pianos unacceptable, whereas I can live with that, and, clearly, a lot of PX purchasers are quite happy with the AP patches as they stand. This, though, is where Nord wins (at 3x the price): you don't like the Yamaha sample? Try the Bosendorfer or the Fazioli. If the PX could load an updated sample set, it would truly be the bee's knees!

Count me as one very happy with the AP sounds on the PX-5S
(and the PX-5S in general). As I said earlier when talking about speakers, it's all very subjective and personal. I do hope the hex-layer AP will cure what ails ya'!

The SuperTooth Disco also looks like it could be a nice option, in terms of size, specs, and price.

If this is the one you are talking about, I like it. The blue LEDs match the PX-5S! Like that retro dial too.

Oh man, I was hoping they could fix that. Unfortunately, once you hear the "plink" you can't un-hear it; and it just gets worse with repeated listening.

Would anyone mind taking measurements of the battery cover/free space available near the battery cover?

The battery cover is about 10 1/2" x 4". You can get away with using a peripheral with a slightly larger footprint. The battery cover has a textured, almost rubberized surface so the grip is good, but I use a little Velcro to make sure my BR-800 stays in place.

Tonight at 7:30pm EST, I'll be doing a LIVE online clinic on the PX-5S. So if you have questions or there is something specific you'd like to see or hear, this is the time. This event will be recorded and then posted over on YouTube afterward. This format relies on your questions...otherwise you'll just see me staring into a camera.

The event will be live at www.ustream.tv/casiomusicgear

When you get there you have to create an ustream account, then to the right of the video there is a Social Stream tab where you can type questions.

I hope to see you there.

Update to my post above:
I found an option in Ustream so I've changed things. There is now a CHAT window next to the video. I removed the "Social Stream". I have also allowed anonymous people in the chat. So you can ask questions without having to link a Facebook or Ustream account.